I don't want to do it under Windows ; please help

[Dan Shimshoni]

Hello,
  Please help me to stay with Linux and not
go back to Windows...
I had stopped using windows about two years ago;
though I have a dual boot , I almost did not
boot into windows in the recent two years.
I am very satisfied with Linux. Everything
that I had in Windows I could get in Linux.
But:
now, I had to prepare some diagrams. I tried
with the "dia" tool. I created a diagram and
converted it to png. The result is reasonable.
However,...
I need to draw some arrows in an angle and
I need to add some text **parallel** to these lines. This means that
the text should not be
vertical or horizontal, but in an anlge (30 or 45).
And it seems that this is **not** possible in dia.

Does any one know a tool with which it can be done?

To be more specific, what I need to do as something
like what is depicted here (and can be done with
visio):
http://www.informit.com/articles/article.aspx?p=1087425&seqNum=21

please look at figure 3.44

I really do **not** want to use visio for it; not unbder windows and
not under some virtual machine
emulating windows and not under wine.

Any ideas ? Is there such a tool in Linux.

I want to stress that the final diagrams shold be
in *.png.

Rgs,
DanS